As the agro-food industries grow worldwide, increasingly large quantities of fruit-processing byproducts are generated as waste accounting for 25-40% of the total fruits processed (Bhushan et al. 2008). These fruit residues, referred to as ‘pomace’, are the pulpy solid remaining after the extraction of juice from fruits, which comprised of peel, seeds, and pulp of the fruit and contain significant quantity of dietary fiber, natural antioxidants, phytochemicals (Balasundram et al., 2006; Yu and Ahmedna, 2013). For instance, around 30-40% apple pomace and 5-11% sludge of the original fruit is generated as a byproduct in a typical cider-processing operation (Gassara et al. 2011). Similarly, grape pomace is a by-product of wine industry accounting for about 20-25% of the weight of the grape crushed for wine production (Yu and Ahmedna 2013). While apple pomace has been used to make citrate, most pomace is viewed as an industrial waste with very little or no economic value and used either as animal feed or returned to farms for composting.
Similarly, the recent phenomenal growth in Greek style yogurt (GSY) has also created a new problem. For every pound of Greek style yogurt, 2-3 pounds of whey is generated as byproduct. Although yogurt whey contains nutritional qualities, it contains fewer solids than conventional cheese whey, which makes it less valuable. The disposal of yogurt whey has become a challenge for the industry. So far, no viable solution has emerged on how to dispose of millions of pounds of GSY whey that is produced every day. Furthermore, whey, especially acid whey, generated during cheese manufacturing also poses disposal problems and its direct use in value-added products of commercial utility would indeed be highly desirable. However, until the present invention, such processes and resulting products have not been developed.
Various fruits and vegetable pomace, including apple and grape pomace, are utilized in extrusion applications (Karkle et al. 2012; Altan et al. 2008b; Khanal et al. 2009b). Extrusion technology is a process of choice to produce a variety of convenience foods due to its versatility, high productivity, low cost, and energy efficiency, and is widely used to enhance the overall digestibility and bioavailability of nutrients (Harper 1981; Brennan et al. 2013). Extrusion is a continuous process that involves high temperature, short time (HTST) cooking, which can decrease spoilage microorganisms and inactivate enzymes. During the process proteins are denatured, starches are gelatinized, and extrudates are texturally restructured (Min et al. 2007). Because extrusion provides a continuous process with mechanical shear to degrade plant cell wall, the insoluble intermolecular network of fruit pomace is disintegrated and the soluble dietary fiber content is improved (Hwang 1998). However, pomace addition decreases the textural qualities of extruded products (Walsh, 2010) and the high-temperature (130-180° C.), high-shear processing conditions used in conventional steam extrusion can also destroy heat sensitive bioactives and nutrients (Onwulata & Heymann, 1994; Alavi & Rizvi, 2009).
Recently, high-temperature steam-extrusion processing has been tried as a means to incorporate fruit and vegetable byproducts in food. However, the high temperatures used led to a loss of nutritional and sensory qualities.
As a part of fruit, the pomace has the potential to be transformed into various ingredients for food applications. For instance, apple pomace, which consists of peel, core and pulp, can be converted into various food and industrial ingredients such as citric acid (Mahawar et al., 2012), pectin (Schieber, 2003); alcohols (Madrera, 2013), bio-adsorbents (Robinson et al., 2002) and biofuels (Vendruscolo et al., 2008). However, the economics of such undertakings is often found to be unattractive for commercialization of the developed processes. As a rich source of dietary fiber and phytochemicals, direct utilization of the pomace in food application can offer an attractive opportunity to both the processors and consumers. Previous attempts to use fruit pomace in various food applications over the past decades (Wang and Thomas 1989; Masoodi and Chauhan 1998; Alavi et al., 2011), to the best of our knowledge, have not materialized into commercial products due its negative impacts on end-product sensory qualities.
Extrusion processing as a means of incorporating fruit and vegetable byproducts in food application is relatively new. However, the effect of pomace addition on end-product sensory or nutritional qualities largely varied depending on extrusion conditions used in processing, pre and post-extrusion treatments, source of the byproduct, etc. However, the conventional cooking extrusion used in all the previous studies is based on high-temperature (130-200° C.) and high-shear (150-300 rpm) operations. Such extreme processing requirements lead to loss of sensory and nutritional qualities and lead to products of undesirable and variable qualities.
The color pigments and bioactive compounds are typically sensitive to high heat and shear used in conventional steam extrusion (Brennan et al., 2011). A wide range of bioactive compound loss (46-90%) has been reported depending on the severity of the conventional steam extrusion (Camire et al., 2007; Khanal et al., 2009a, White et al., 2010). For instance, only 35% of the total anthocyanin present in the cranberry pomace were retained at high barrel temperature (190° C.) and screw speed (200 rpm); the retention was increased to 54% when the barrel temperature was reduced to 150° C. (White et al., 2010), however, the study did not indicate the physical characteristics or textural qualities of the final extruded products. Camire et al., (2007) reported a 90% loss of anthocyanin for extrusion cooking of various fruit powders. The losses are mainly due to high temperature (170° C.) and shear (175 rpm) used in the extrusion. Generally, the phenolic acids are decarboxylated and condensed into tannins at high temperature processing (Brennan et al., 2011).
U.S. Pat. No. 8,877,277 to Ganjyal and the related U.S. Patent Application Publication No. US 2013/0287922 to Ganjyal (collectively the “Ganjyal disclosures”) are directed to a method of making a food product by forming an expanded extrudate using a supercritical fluid extrusion process, as well as to the supercritical fluid extruded food product produced by the method, but restricted to formulations with starch having very specific viscosity requirements. The Ganjyal disclosures mention that fruit- and vegetable-based ingredients can be used in the method, and that proteins such as whey proteins can also be mixed into various ingredient formulations. However, the Ganjyal disclosures mention that post-extrusion processing (e.g., post-extrusion vacuum drying) was needed when using fruit pomace such as cranberry powder (pomace) in the extrusion process. Further, in every instance, the Ganjyal disclosures described the use of a separate hydration step (i.e., adding water) during the supercritical fluid extrusion process. There is no mention or suggestion to forego this hydration step, and no mention of using liquid whey byproduct or even milk protein concentrate (MPC) as ingredients in the supercritical fluid extrusion process.
U.S. Pat. No. 7,220,442 to Gautam et al. (“Gautam”) is directed to a process for preparing a nutrition bar from non-soy proteins using supercritical fluid extrusion. Gautam teaches that the non-soy proteins can be from sources such as whey protein, particularly whey protein isolates and whey protein concentrates. The supercritical fluid extrusion process of Gautam also requires a separate water hydration step, including adding water to the whey protein isolates or the whey protein concentrates. Gautam does not describe or suggest the use of liquid whey byproduct as an ingredient in the supercritical fluid extrusion formulations, and certainly fails to teach or suggest that a liquid whey byproduct can be used in lieu of water as a source of hydration in the supercritical fluid extrusion process.
The present invention is directed to overcoming these and other deficiencies in the art.